Coating continuous

Air-bubble entrapment may occur in the case of a gravity-appHed continuous coating over an impermeable substrate. Bubbles may also be caused by moisture vaporization from the substrate. Remelting of the coating may minimize the bubble defects. Curtain coating equipment of this design is capable of operation at substrate speeds up to 500 m /min. 

Fluxes also contain agents that faciHtate appHcation, such as petroleum jeUy or alcohol. These bum or evaporate at elevated temperatures before the soldering temperature is attained, leaving behind a uniform coating of flux. Fluxes become molten before the joining process is reached. The molten flux flows or spreads to form a continuous coating over the surfaces to which they have been appHed. 

Tin is anodic to steel in alkaline solutions, the corrosion rate for a continuous coating being similar to that of pure tin, and tinned articles that are washed in aerated alkaline detergents slowly lose their coating. 

Nitrocellulose alone will not give a continuous coating. It must, therefore, be blended with other components comprising a plasticiser and a hardening resin. An extensive range of such products is available, the ultimate choice depending on the properties required. 

A spray coating of aluminum on a steel is not likely to spall or flake, but the coating is usually not continuous and may leave some areas of the steel unprotected. Hot-dipped aluminized steel gives a continuous coating and has proved satisfactory in a number of applications. 

Fig. 51. Scanning electron microscope image of different stages of metalization of DNA. (a) Linear chain of separated palladium clusters connecting two gold contacts (b) magnification of (a) showing clusters with diameter > 40 nm (c) continuous coated DNA strand after one development step with a diameter larger than 40 nm. Reproduced with permission from Ref. (175). Copyright 2001, American Institute of Physics.

To protect steel piping and wire we can powder coat it with a layer of nylon 11. The powder coating process consists of immersing metal heated to above the melting point of nylon II (approximately 190 °C) in a fluidized bed of the polymer powder. When the polymer powder comes into contact with the heated metal, it melts and fuses to form a continuous coating. Powder coated products include hospital bed frames, shopping trolleys, and dishwasher racks. 

On the other hand, if ysw Yew. the precipitate tends to form a structurally continuous coating on the substrate grain. The interfacial energy (Eq. 6.16) may even become negative and the activation barrier vanishes. An example reflecting this condition is the growth of amorphous silica on the surface of quartz (Wollast, 1974). 

Continuous coating can be obtained by roll coating or spreading. There are three main versions ... 

Riimpler, K. and Jacob, M., Continuous coating in fluidized bed, Food Marketing Tech., 12 (1998) 41-43. 

Continuous Coating Processes Based on Existing Film-Coating Technologies... 

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